Field of the Invention
The present invention relates to a wafer polishing apparatus.
Discussion of the Related Art
In a double side polishing (DSP) process, a wafer may be polished through friction between pads and the wafer using a slurry as an abrasive by pressing surface plates and flatness of the wafer may be determined.
The DSP process may be executed by chemical-mechanical polishing through a chemical process using chemical action between a slurry and the surface of a wafer and a mechanical process using friction between pads and the wafer by pressing surface plates.
In general, the shape of an upper surface plate and a lower surface plate of a polishing apparatus may be processed in advance prior to a polishing process according to the size of a wafer and an application method.
FIGS. 23A to 23C illustrate upper surface plates and lower surface plates having various shapes.
FIG. 23A illustrates an upper surface plate 11 having a lower surface, the central part of which is concave, and a lower surface plate 12 having an upper surface, the central part of which is convex, FIG. 23B illustrates an upper surface plate 11a having a lower surface, the central part of which is convex, and a lower surface plate 12a having an upper surface, the central part of which is concave, and FIG. 23C illustrates an upper surface plate 11b having a lower surface, the central part of which is convex, and a lower surface plate 12b having an upper surface, the central part of which is convex.
If an upper surface plate and a lower surface plate are used at a high pressure for a long time, the shapes of the initially processed upper and lower surface plates may be modified and, thus, re-processing of the shapes of the upper surface plate and the lower surface plate may be required. In order to change the shapes of the upper surface plate and the lower surface plate, the upper surface plate and the lower surface plate are detached from the polishing apparatus and then the detached upper and lower surface plates are re-processed to have desired shapes. In order to change the shapes of the upper surface plate and the lower surface plate, operation of the polishing apparatus needs to be stopped for a long time, thus causing economic loss.